A U.S. Navy MH-53E Sea Dragon helicopter prepares to land on a flight deck. / MC2 Blake Midnight, U.S. Navy, via AP

by Michael Winter, USA TODAY

by Michael Winter, USA TODAY

VIRGINIA BEACH - Two U.S. sailors died Wednesday and a third was missing after their minesweeper helicopter went down in the Atlantic Ocean during routine training off Virginia, the Navy said.

Two other crewmembers were being treated for injuries at a Norfolk hospital.

Officials said a Navy helicopter rescued four crewmembers about 20 miles off Cape Henry after their MH-53E Sea Dragon went down about 11 a.m. One was declared dead soon after arriving at Norfolk Sentara General Hospital, and the second sailor died hours later, the Navy said Wednesday night.

The Coast Guard and Virginia Beach fire boats were aiding the search for the missing sailor, which was to continue throughout the night.

The Navy said the identifies of the crewmembers would not be released until 24 hours after their families are notified.

Navy officials said the helicopter was one of two Sea Dragons assigned to the Helicopter Mine Countermeasures Squadron 14 at Norfolk Naval Station that were training. One issued a distress call about 15 minutes before it slammed into the 42-degree water. The second helicopter dropped a life raft, and two sailors climbed in, a Navy spokesman toldThe Virginian-Pilot.

The Navy did not reveal the nature of the distress call.

Officials said the 87-foot patrol boat Shearwater, out of Portsmouth, a small boat from Station Little Creek and two MH-60S helicopters responded about 11:45 a.m. A Virginia Beach fire boat was assisting the military, officials said.

Meteorologist Evan Stewart said the air temperature about 30 degrees at the time of the crash.

Debris was scattered over a half mile, a Virginia Beach fire official told the Virginian-Pilot, and search crews had located the fuselage and tail.

The Sea Dragon, built by Sikorsky, is a modified version of the more common CH-53E Super Stallion and can operate from aircraft carriers or other warships. Primarily used to clear mines from shipping lanes, it also delivers heavy equipment to and from ships and can transport up to 55 combat troops.

At 99 feet long, the Sea Dragon is the largest helicopter in the Western world.

A July 2012 crash of another Sea Dragon killed two of five crewmembers during an attempt to retrieve a downed helicopter belonging to the Royal Air Force of Oman. A Navy investigation blamed the Norfolk-based crew for not conducting preflight safety checks and not having an established plan for aborting the mission in the mountains outside Muscat, the capital.